Saturday, July 21, 2012

Lab Tour, part 2 - Electronics Assembly/Test

This is the second post in my "Lab Tour" series. If you haven't read the first one, it's here.

As with last time I'll begin with an overview of the work area. It consists of two back-to-back workbenches that are typically used in tandem.

Assembly and test bench

The first bench is used for component placement prior to reflow soldering, as well as testing boards after assembly. A dedicated lab computer is located here for reading schematics and datasheets while working. Unfortunately it's not fast enough to run an FPGA toolchain but I intend to replace it with something that can do so in the future.

I have a grounded mat plus a wrist strap for working at this bench, grounded through the earth terminal of my benchtop power supply.

Close-up of test equipment

My only other piece of test equipment at the moment is my Rigol DS1102D 100MHz mixed-signal oscilloscope. I'm looking into getting a function generator at some point but much of my disposable income lately has been going into FPGAs and board fab so it'll have to wait a while!

Just off the right side of the frame is my cheap 10x/30x stereo inspection microscope from Premiere. It's proved invaluable for checking the quality of component placement and looking for shorts, as well as just providing a close-up view when manually applying solder paste or placing components.

Through-hole component inventory

I keep all of my SMT components in drawers of this bench, but the through-hole parts are too big so they have to go on top. This is the oldest part of my lab by far - I've had these organizers since I was 10 or 11 years old and many of the passive components date almost that far back.

Soldering bench

The second bench is used for hand soldering through-hole components, rework, and cleaning of boards.

Soldering equipment

All of my soldering equipment is made by Aoyue, a cheap Chinese clone (right down to the model numbers!) of Hakko designs. They've worked fine for me so far.

If you look closely at the full resolution frame you can see that the left-hand iron is labeled "SAC305 ONLY" and the right hand is labeled "LEAD ALLOYS ONLY". I try to avoid mixing solder alloys when I can, and rather than swapping tips it's easier to have two identical irons. The majority of my work is lead-free but occasionally I find it necessary to rework an older board using 63/37.

The hot air pencil is absolutely indispensable for SMT soldering. It allows me to reflow a single component during rework without putting the entire board in the oven, getting much nicer looking joints than I would if I used an iron as well as taking advantage of the self-aligning properties of the reflow process. It's also about the only way to remove a large QFP intact.

Just visible at the right side of the frame is an activated-charcoal solder fume extractor. While I do work in a large room with good ventilation, it's a lot harder to replace your lungs than a TSSOP so I prefer to err on the side of caution ;)

Solvent tray

I almost always use no-clean rosin fluxes but it's still handy to have a way of removing excess from a board, or cleaning dirt off a board that's been sitting around for a while. For this I have a selection of various solvents ranging from distilled water to acetone to alcohols, as well as water-based detergents from Alconox. I don't have an ultrasonic cleaner at the moment but I plan to add one to the wet bench in a few months.